1. Technical Field
Embodiments consistent with the present invention are related to conductive liquid sensors. In particular, some embodiments consistent with the present invention are related to measuring a level of an electrolyte in a holding tank of a flow battery system.
2. Discussion of Related Art
Fluids in a system often have important dynamic properties which are important to the overall operation of a system. Accordingly, sensors have been developed which measure these dynamic properties to monitor the state of the system. One such system is a reduction-oxidation (redox) flow battery system.
A redox flow battery is an electrochemical storage device in which an electrolyte containing one or more dissolved electro-active species flows through a reactor cell where chemical energy is converted to electrical energy. Conversely, the discharged electrolyte can be flowed through a reactor cell such that electrical energy is converted to chemical energy. Electrolyte is stored externally, for example in tanks, and flowed through a set of cells where the electrochemical reaction takes place. Externally stored electrolytes can be flowed through the battery system by pumping, gravity feed, or by any other method of moving conductive liquid through the system. The reaction in a flow battery is reversible. The electrolyte can be recharged without replacing the electroactive material. Hence, the energy capacity of a redox flow battery is related to the total electrolyte volume (i.e., the size of the storage tank). Electrolytes in the system have a constantly changing level, which may need to be monitored.
Capacitive-type level sensors are one type of sensor. Capacitive-type sensors require an RF excitation, and do not have any conductive contact with the electrolyte. Resistive-type level sensors are another type of sensor. Typical resistive-type level sensors measure the level of the electrolyte or other conductive liquid by monitoring the resistance of the conductive liquid. However, conventional resistive-type sensors can only measure whether or not an electrolyte is at a predetermined level. Moreover, resistive-type sensors typically use highly metallic electrodes, which quickly corrode in the corrosive electrolyte, resulting over time, in inaccurate measurements. Furthermore, capacitive and resistive electrolyte level sensors typically are only capable of measuring a level, such that flow battery systems require additional sensors for determining other parameters such as the temperature of an electrolyte.
There is therefore a need for a conductive liquid-level sensor that is able to withstand a corrosive environment and provide an accurate measurement of the level of a conductive liquid.